Add ability to filter issues by their pinned status in bd list command.
- Add pinned column to issues table via migration 023
- Add Pinned field to Issue struct and IssueFilter
- Update all storage layer queries to include pinned column
- Add --pinned flag to show only pinned issues
- Add --no-pinned flag to exclude pinned issues
- Update RPC layer to forward pinned filter to daemon mode
- Add pinned to allowedUpdateFields for bd update support
Resolves: beads-p8e
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>